The pathogenesis of viral gastrointestinal and respiratory infections in man, with particular emphasis on cell mediated immunity is being examined. Influenza infections result in virus specific cell mediated immune responses as measured by virus specific in in vitro lymphocyte blastogenesis and lymphocytotoxicity. These responses may be mediated by hemagglutinin receptors on human lymphocytes. A new interferon inducer, PICLC, appeared to be non-toxic when administered intranasally to volunteers, but had no effect on experimentally induced rhinovirus infection. Viral gastroenteritis induced by the parvovirus-like agents appeared to induce the production of local antibodies to the agents in gastrointestinal secretions. Human parvoviruses (adenovirus-associated viruses) are potentiated in vitro by tissue culture cells chronically infected with herpes simplex virus or transformed by adenovirus.